Very difficult, if not impossible, to enforce sanctions against non-complying third parties that RESELL tech to Iran, and even to ensure compliance within your own country. The US Treasury Department's Office of Foreign Assets Control only has 250 people ensuring compliance with all sanctions worldwide. They need more.

And the EU doesn't even have an organization for that. All they have is a still pending Sanctions Envoy. Think of what leaks through with so little policing. Only individual member-states have any kind of meaningful mechanisms to address that.